Morphological and molecular studies of Mallomonas species from section Multisetigerae (Chrysophyceae, Synurales) with description of a new species

This research is devoted to the study of Mallomonas species from the section Multisetigerae in a tropical region (Vietnam and the Philippines) using electron microscopy and molecular studies. For the first time, molecular data and phylogenetic relationships for species within this section are presented. Analysis of six algal cultures, based on a combined dataset of SSU rDNA and <i>rbc</i>L genes, as well as the ITS1-5.8S-ITS2 rDNA region, revealed three distinct clades. Notably, these clades did not form a monophyletic grouping. Two of the studied cultures were identified as <i>Mallomonas multisetigera</i>, and another two as <i>M. neoampla</i>. For the remaining clade, we describe a new species, <i>Mallomonas rutabuliformis</i> <b>sp. nov.</b>, which combines morphological features of fossil and modern taxa. The study also synthesizes original and literature data on the distribution of the <i>Mallomonas multisetigera</i> morphotype.